OLED devices on the one hand and inorganic electroluminescent devices on the other hand, i.e. organic electroluminescent films on the one hand and inorganic electroluminescent films on the other hand, are based on the effect that a light-emitting layer between two electrode layers is electrically stimulated by the electrode layers to emit light. In inorganic electroluminescent films the two electrodes are electrically insulated from each other and function as the two halves of a capacitor. When applying an alternating voltage to this capacitor it emits an electric field which stimulates the light-emitting layer to emit light. In contrast, in OLED devices, i.e. organic electroluminescent films, a direct current flows from one electrode to the other, thereby passing through the light-emitting layer which then, again, emits light.
The construction of OLED devices is generally a time-consuming process which needs a high precision of application steps of different functional layers such as the two electrodes (anode and cathode) and the organic light-emitting layer. The OLED device must be properly sealed against outside influences in order to achieve a sufficient lifetime and it must be assembled on a carrier which is sufficiently moisture-resistant and stable. Preferably, this carrier is flexible in order to provide for an overall flexible OLED device. This firstly has the advantage that the OLED device is considerably thin so that it can be applied in all such environments in which larger thicknesses of lighting solutions must be avoided. Secondly, a flexible OLED device can also be applied in such circumstances in which the OLED device is not arranged along a purely even plane, but rather along a curved plane or the like.
One possible solution to realize a flexible carrier substrate would be to use a metal film or foil as shown in U.S. Pat. No. 6,911,666 B2. However, this has a major drawback which needs to be circumvented for operational reasons of the OLED: metal films or foils can generally be characterized as conductive substrates which means that their own conductivity may dangerously interfere with other functional layers of the OLED device such as the ones named above. In essence, the electrical conductivity of such conductive carrier substrate may lead to short circuits. As both the anode and the cathode need to be electrically contacted via contact pads on the carrier substrate, one needs to realize a contact pad for one of the electrodes which is galvanically insulated from the other electrode.
This can either be realized by applying a non-conductive coating to the top of the conductive carrier substrate over the complete surface of the carrier substrate plus separated conductive coatings on top of the non-conductive coating or by locally depositing an insulating material in the area of one electrode contact pad. In the first case, the current can only be drawn across the non-conductive coating layer—in other words the conductivity of the carrier substrate is not used for transporting current. This solution also limits the choice of materials and leads to rather thick layer structures for large area OLED devices. In the second case, an inorganic material needs to be deposited as the contact pad on the insulating material needs to be in contact with the inner electrode of the OLED device and with an external power supply—which means the contact pad crosses the encapsulation of the OLED device. A patterned deposition of such an insulating layer or a post patterning process is also costly and rather ineffective. Organic insulators cannot be used as the cannot act as a moisture barrier which thus would lead to operational defects of the OLED device rather quickly.
Therefore, it is an object of the invention to provide for a possibility of more effectively providing an OLED device with a conductive carrier substrate, in particular for producing it with less elaborate coating steps than previously necessary.